page_title: Madison Symmetric Torus
section_title: Classification
hierarchical_section_title: Madison Symmetric Torus / Classification
caption_attribution_description: English: This is a picture of the geometry inside the Madison Symmetric Torus. The minor radius is 0.53 meters. The major radius is 1.5 meters. The torus is a 0.05 meter thick. There are two currents inside the device. First, a toroidal current runs around an iron core and second, a Poloidal current running inside the skin of the torus. Source: Almagri, A. F., S. Assadi, S. C. Prager, J. S. Sarff, and D. W. Kerst. "Locked Modes and Magnetic Field Errors in the Madison Symmetric Torus." Physics of Fluids B: Plasma Physics 4.12 (1992): 4080. Other information This is a picture of the geometry inside the Madison Symmetric Torus. The minor radius is 0.53 meters. The major radius is 1.5 meters. The torus is a 0.05 meter thick. There are two currents inside the device. First, a toroidal current runs around an iron core and second, a Poloidal current running inside the skin of the torus. Source: Almagri, A. F., S. Assadi, S. C. Prager, J. S. Sarff, and D. W. Kerst. "Locked Modes and Magnetic Field Errors in the Madison Symmetric Torus." Physics of Fluids B: Plasma Physics 4.12 (1992): 4080.
context_page_description: The Madison Symmetric Torus is a reversed field pinch physics experiment with applications to both fusion energy research and astrophysical plasmas located at University of Wisconsin-Madison. RFPs are significantly different from tokamaks in that they tend to have a higher power density and better confinement characteristics for a given average magnetic field. RFPs also tend to be dominated by non-ideal phenomena and turbulent effects. MST is one of the sites in the Center for Magnetic Self Organization.
context_section_description: As in most such experiments the MST plasma is a toroidal pinch, which means the plasma is shaped like a donut and confined by a magnetic field generated by a large current flowing through it. MST falls into an unconventional class of machine called a reversed field pinch (RFP.) The RFP is so named because the toroidal magnetic field that permeates the plasma spontaneously reverses direction near the edge.
  A reversed field pinch is formed similarly to other toroidal pinch devices, by driving current through the plasma from an associated capacitor bank or other high-current power source. In a tokamak the toroidal field is much stronger than the poloidal field, but in an RFP it's just the opposite. In fact, in an RFP the externally applied toroidal field is switched off shortly after startup. The plasma in an RFP is also much closer to the wall than in a Tokamak. This permits a peculiar arrangement of the magnetic field lines, which will 'relax' into a new state such that the total magnetic energy in the plasma is minimized and the total magnetic helicity is conserved. The relaxed state, called a Taylor state, is marked by a peculiar arrangement of magnetic field lines where the toroidal magnetic field at the edge spontaneously reverses direction.
caption: The geometry inside the Madison Symmetric Torus.[1]
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